The fertile phase in a mammal can be defined as the period during which sperm present in the uterus may encounter and fertilize an egg. Generally, in female humans, the average reproductive cycle is 28 days, of which a released egg survives only about 12 to 24 hours. However, the uterus is capable of storing sperm for a period of up to four days. Thus, the fertile phase can commence up to four days prior to ovulation and last for up to one day after ovulation. But, the time period following ovulation, when an egg is released, is relatively narrow.
Many prior art devices have been proposed to determine when ovulation has occurred. However, by merely determining when ovulation has occurred, these prior art devices and methods only determine a fraction of the fertile phase in a female human. Clearly, an advantage can be obtained by predicting ovulation at least four days in advance, which will encompass the entire fertile phase of a woman. In this way, pregnancy can be planned.
Several methods for determining ovulation have been proposed in the past. In female humans, the maturation of ovarian follicles which will eventually release a fertile egg are effected by the action of Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) secreted by the anterior lobe of the pituitary. The ovulatory phase of the menstrual cycle is preceded by a significant rise in serum total estrogens 24 to 48 hours prior to ovulation, which prepare the uterus for possible implantation. The rise in estrogens is followed by a rapid rise in serum luteinizing hormone (LH) reaching a peak 12 to 24 hours prior to ovulation. Many other physiological conditions also change around the time of ovulation. For instance, basal body temperature (BBT) reaches a nadir followed by a sharp rise around the time of ovulation. Cervical mucus undergoes viscosity changes stimulated by rising estrogen which can help direct sperm towards the egg.
Several fertility detectors have been developed which measure these various hormones or their indirect physiological effects. The BBT method, referred to above, generally requires female humans to take their vaginal temperature and chart the value every morning before rising. Besides the considerable diligence involved, the method is generally only accurate within one to two days of ovulation, and gives no prior notice. Cervical mucus measurements have been regarded as somewhat more helpful. Women can examine their cervical mucus for a thinning of the mucus just before ovulation, which allows it to be drawn intact between the fingers and is referred to as the spinbarkeit reaction. Another method involves examining the cervical mucus under a microscope and looking for a “ferning” reaction indicative of imminent ovulation. A further method measures vaginal mucus conductivity using impedance probes which allows a somewhat more quantitative estimation of the mucus changes as disclosed in U.S. Pat. No. 4,770,186 . U.S. Pat. No. 5,209,238 to Sundhar discloses an ovulation monitor which determines the presence of a viable egg by sensing the mucous density, basil body temperature, and pH level and LH level of secretion in the vagina.
However, these prior art methods suffer from the disadvantage that they determine ovulation, but do not provide a means for predicting ovulation, thereby missing a large portion of the fertile phase. Also, cervical mucus examination suffers from subjective errors as well as being arduous and again gives little to no prior notice of ovulation.
U.S. Pat. No. 5,685,319 to Marett discloses that a significant pH nadir in female eccrine sweat was found to occur approximately five to six days prior to ovulation. In this way, tracking the pH of eccrine sweat could assist in predicting ovulation, and thereby determining the fertility status of a female human. Furthermore, an advantage of tracking pH is that it is inherently buffered in that the hydrogen ions H+ can react with the hydroxide ion (OH) to form water. In addition, even though there is no satisfactory mechanism to explain skin acidity, previous studies have found that eccrine sweat of women is also generally buffered by either the lactic acid/lactate system, free amino acid secretion or CO2 bicarbonate. The benefit of having the pH buffered is that changes in the quantity of eccrine sweat, such as through evaporation or increased physical activity, will not greatly affect the pH, thereby avoiding spurious readings.
Several researchers have also investigated changes of other ions in eccrine sweat. For instance, Lieberman and Taylor looked at chloride (Cl−), sodium (Na+) and potassium (K+) in the eccrine sweat of female humans (Lieberman et al. JAMA Feb. 21, 1996 , Vol. 195, No. 8, pages 117-123 and Taylor et al., Journal of Investigative Dermatology, Vol. 53, No. 3, pages 234-237, 1969). However, neither Lieberman nor Taylor investigated changes in the concentrations of these ions prior to ovulation and for the purpose of predicting ovulation.
One disadvantage of much of the prior art has been that it fails to predict ovulation at least three to six days in advance. Because of this, the prior art methods and devices fail to determine the entire fertile phase of a female.
Furthermore, other than for measuring pH, the prior art has failed to consider what other characteristics of eccrine sweat of female humans can be used to predict ovulation. The prior art has failed to provide a reliable and consistent method and device to obtain measurements of the characteristics of eccrine sweat, such as changes in the concentrations of ions, other than pH. In addition, the prior art has failed to provide a method and device which can measure changes in concentrations of ions in eccrine sweat which are not naturally buffered, as is pH, and which may therefore vary due to other factors, such as eccrine sweat volume due to increased physical activity, ambient temperature or evaporation.
Accordingly, there is a need in the art for a method and device to reliably and economically predict ovulation three to six days in advance in order to determine a larger portion of the fertile phase of a female mammal, and preferably a female human. There is also a need for a method and device to predict ovulation which is easy to use, reliable and inexpensive.